Slider inside HBox : centering and spacing issues

I am going to assume that a Slider cannot go inside a CompositeField because the Designer won't let it happen.
So I'm putting one, along with two other components, inside an HBox. I want them to be centered with a little space between each:

{abcDisplayField} {Number Field} {Slider}

I've wrapped the HBox in a container and am applying CSS to the wrapper to center its contents. When the contents are centered, they're shifted to the left, as if the centering algorithm were working with a slider width that is much greater than it actually is.

Please see the "flex" (for sizing) and "pack" (for centering) layout options for HBox in the documentation. Setting "pack" to "center" will center your items in the HBox layout. You can then apply a "margins" configuration to space out your items.